Predictive value for progression to tuberculosis by IGRA and TST in immigrant contacts

Abstract

The authors determined the positive predictive value (PPV) for progression to tuberculosis (TB) of two interferon-γ release assays (IGRAs), QuantiFERON-TB® Gold In-tube (QFT-GIT) and T-SPOT.TB®, and the tuberculin skin test (TST) in immigrants contacts.Immigrant close contacts of sputum smear-positive TB patients were included when aged ≥16 yrs and their TST result was ≥5 mm 0 or 3 months after diagnosis of the index patient. Contacts were followed for the next 2 yrs for development of TB disease.Of 339 immigrant contacts with TST ≥5 mm, 324 and 299 had valid results of QFT-GIT and T-SPOT.TB®, respectively. Nine contacts developed active TB. One patient had not been tested with TST, while another patient had not been tested with QFT-GIT and T-SPOT.TB®. The PPV for progression to TB during this period was 9/288 = 3.1% (95% CI 1.3–5.0%) for TST ≥10 mm, 7/184 = 3.8% (95% CI 1.7–5.9%) for TST ≥15 mm, 5/178 = 2.8% (95% CI 1.0–4.6%) for QFT-GIT and 6/181 = 3.3% (95% CI 1.3–5.3%) for T-SPOT.TB®. Sensitivity was 100%, 88%, 63% and 75%, respectively.The predictive values of QFT-GIT, T-SPOT.TB® and TST for progression to TB disease among immigrant close contacts were comparable.